Optical communications Systems at 10 Gb/s, 40 Gb/s and emerging higher bit-rates have stringent requirements on the characteristics of the optical pulses. Impairments to the pulsestream caused by group velocity dispersion (GVD), polarization mode dispersion (PMD), and other undesired effects can severely degrade these systems. The ability to affordably and dynamically measure these time-varying impairments, either for monitoring or compensating purposes, adds attractive functionality to a transmission network. The need for these techniques exists both at the receiver and at individual repeater locations throughout the network.